1. Field of the Invention
The present invention relates to a process for producing nitrile compounds by reacting carbocyclic or heterocyclic compounds with a mixed gas of ammonia and oxygen.
2. Description of the Prior Art
Aromatic nitriles produced by ammoxidation of carbocyclic compounds are useful as raw materials for manufacturing synthetic resins, agricultural chemicals, etc., and as intermediate materials for producing amines, isocyanates, etc. Heterocyclic nitriles produced by ammoxidation of heterocyclic compounds are also useful as intermediates of medicines, animal feed additives, food additives, etc.
Ammoxidation of carbocyclic or heterocyclic compounds to aromatic or heterocyclic nitrile compounds generates a larger amount of heat as compared to ammoxidation of olefins. Therefore, a vapor-phase fluid catalytic reaction has been advantageously used for the ammoxidation of carbocyclic or heterocyclic compounds because the heat of reaction can be easily removed and side reactions due to local heating can be avoided. Various catalyst systems comprising a metal oxide or comprising a metal oxide supported on a carrier such as silica and alumina have been proposed for use in the vapor-phase fluid catalytic reaction.
For instance, Japanese Patent Publication No. 49-45860 produces an aromatic nitrile by ammoxidation of an alkyl-substituted aromatic compound in the presence of a catalyst containing V, Cr and B. Japanese Patent Application Laid-Open No. 49-13141 conducts the similar reaction in the presence of a catalyst containing Fe, Bi and Mo. Japanese Patent Application Laid-Open No. 63-190646 discloses ammoxidation of an alkyl-substituted aromatic compound or an alkyl-substituted alicyclic compound using an Fexe2x80x94Sb catalyst.
Japanese Patent Application Laid-Open No. 1-275551 discloses ammoxidation of an alkyl-substituted aromatic compound or an alkyl-substituted heterocyclic compound in the presence of a Vxe2x80x94Crxe2x80x94Bxe2x80x94Mo catalyst. Japanese Patent Application Laid-Open No. 5-170724 conducts the similar reaction in the presence of an Moxe2x80x94P catalyst. Japanese Patent Application Laid-Open No. 9-71561 produces dicyanobenzene by ammoxidation of xylene in the presence of an Fexe2x80x94Sbxe2x80x94V catalyst.
These known processes are advantageous because aromatic or heterocyclic nitriles are produced in high yields. However, the catalysts used in the processes are decreased in their activity with time. Therefore, it has been demanded to produce nitrile compounds in high yields over a long period of time. To meet the demands, there have been proposed a method for inhibiting the catalyst deterioration in fluidized reaction, a catalyst with little activity change with time, etc. For instance, Japanese Patent Application Laid-Open No. 10-120641 teaches to prevent the deterioration of a metal oxide catalyst containing V and/or Mo by a controlled feeding of raw materials to a fluid reactor.
As described above, in the process for producing nitrile compounds by fluid catalytic ammoxidation of carbocyclic or heterocyclic compounds in vapor-phase, various attempts have been made to improve catalysts and apparatuses for preventing deterioration of the catalysts. However, it is still demanded to produce the nitrile compounds stably in high yields over a prolonged period of time.
It is an object of the present invention to provide an economical process for producing a nitrile compound by vapor-phase fluid catalytic reaction of a carbocyclic or heterocyclic compound with ammonia and an oxygen-containing gas in high yields with little lowering with time over a long period of time.
As a result of extensive researches and studies on the production of nitrile compounds in view of the above objects, the inventors have found that one of the attributing causes of the deterioration of catalyst activity is water accompanying unreacted ammonia during its recycle and reuse, and that the use of catalysts containing a specific amount of alkali metal enables the ammoxidation to be stably performed with little change with time in the yields over a long period of time. The present invention has been accomplished based on this finding.
Namely, in accordance with the present invention, there is provided a process for producing an aromatic or heterocyclic nitrile, comprising a step of subjecting a carbocyclic or heterocyclic compound, ammonia and an oxygen-containing gas to fluid catalytic reaction in vapor phase in the presence of a catalyst containing 0.10 to 0.40% by weight of alkali metal; and a step of recycling unreacted ammonia recovered from a reaction product gas.
The present invention will be described in detail below.
In the vapor-phase catalytic reaction of the present invention, a carbocyclic compound or a heterocyclic compound is reacted with an oxygen-containing gas and ammonia. To effectively remove heat of reaction and avoid side reactions due to local heating, the catalytic reaction is carried out in fluidized manner.
The carbocyclic compounds used as raw materials in the present invention has a carbon ring selected from the group consisting of benzene, naphthalene, anthracene, cyclohexene, cyclohexane, dihydronaphthalene, tetralin and decaline. The carbon ring has at least one nitrile-forming group selected from the group consisting of methyl, ethyl, propyl, formyl, acetyl, hydroxymethyl and methoxycarbonyl. Further, the carbocyclic compound may have another substituent such as halogen atom, hydroxyl, alkoxyl, amino, nitro, etc. Examples of the carbocyclic compounds include toluene, xylene, trimethylbenzene, ethylbenzene, methylnaphthalene, dimethylnaphthalene, methyltetralin, dimethyltetralin, chlorotoluene, dichlorotoluene, methylaniline, cresol and methylanisole.
The heterocyclic compounds used in the present invention have at least one hetero ring selected from the group consisting of furan, pyrrole, indole, thiophene, pyrazole, imidazole, oxazole, pyran, pyridine, quinoline, isoquinoline, pyrroline, pyrrolidine, imidazoline, imidazolidine, piperidine and piperazine. The hetero ring has at least one nitrile-forming group selected from the same group as described above for the carbocyclic compounds. Examples of the heterocyclic compounds include furfural, 2-methylthiophene, 3-methylthiophene, 2-formylthiophene, 4-methylthiazole, methylpyridine, dimethylpyridine, trimethylpyridine, methylquinoline, methylpyrazine, dimethylpyrazine and methylpiperazine.
The ammonia used as a raw material in the present invention may be of industrial grade. The amount of ammonia used is 1.5 to 10 moles, preferably 3 to 5 moles per one mole of the nitrile-forming group in the carbocyclic or heterocyclic compound. When the amount of ammonia used is less than the above range, the yield of the nitrile compound is lowered. When the amount of ammonia used exceeds the above range, the space time yield of the nitrile compound becomes small.
In the process of the present invention, the unreacted ammonia in reaction product gas is recovered and recycled to the reaction system for reuse. The method of recovering the unreacted ammonia from the reaction product gas is not particularly restricted. From an industrial viewpoint, it is suitable that the unreacted ammonia is absorbed in water, and then separated from by-products by distillation.
The oxygen-containing gas used in the present invention may be usually air. Alternatively, diluted air or oxygen with an inert gas such as nitrogen, carbon dioxide or waste gases may also be used as the oxygen-containing gas. The oxygen concentration in the oxygen-containing gas is preferably 10 to 20% by volume. The amount of oxygen used is 1.5 moles or larger, preferably 2 to 50 moles per one mole of the nitrile-forming group in the carbocyclic or heterocyclic compound. When less than the above range, the yield of the nitrile compound is lowered. When exceeding the above range, the space time yield of the nitrile compound becomes small.
The catalyst used in the present invention contains an alkali metal in an amount of 0.1 to 0.4% by weight, preferably 0.1 to 0.3% by weight based on the weight of a supported catalyst (total weight of the catalyst and carrier).
When the content of the alkali metal is less than the above range, the catalyst is poor in mechanical strength such as wear resistance (attrition resistance). When the content exceeds the above range, the sintering of the catalyst proceeds by interaction between water in the raw materials and the alkali metal in the catalyst, resulting in the reduction with time of yields of the nitrile compound.
The process of the present invention is preferably performed in the presence of a catalyst comprising at least one oxide selected from the group consisting of oxides of V, Mo and Fe.
In addition to the oxides of V, Mo and Fe, the catalyst may further contain at least one oxide selected from the group consisting of oxides of Mg, Ca, Ba, La, Ti, Zr, Cr, W, Co, Ni, B, Al, Ge, Sn, Pb, P, Sb and Bi. Such a catalyst is represented by the formula:
(V)a(Mo)b(Fe)c(X)d(Y)e(O)f
wherein X is at least one element selected from the group consisting of Mg, Ca, Ba, La, Ti, Zr, Cr, W, Co and Ni; Y is at least one element selected from the group consisting of B, Al, Ge, Sn, Pb, P, Sb and Bi; and subscripts a, b, c, d and e represent atomic proportions, a being 0.01 to 1, preferably 0.1 to 0.7; b being 0.01 to 1, preferably 0.05 to 0.7; c being 0 to 1, preferably 0.05 to 0.7; d being 0 to 1, preferably 0.05 to 0.7; e being 0 to 1, preferably 0.05 to 0.7 and f being the number of oxide-forming oxygen atoms.
Of the metal oxide catalysts, preferred are Vxe2x80x94Crxe2x80x94Bxe2x80x94Moxe2x80x94Pxe2x80x94(Na and/or K) metal oxide catalysts. Examples of the vanadium sources may be inorganic salts of vanadium such as ammonium salts and sulfates, and vanadium salts of organic acids such as oxalic acid and tartaric acid. Examples of the molybdenum sources may be ammonium molybdate, phosphomolybdic acid, ammonium phosphomolybdate and molybdenum salts of organic acids such as oxalic acid and tartaric acid. Examples of the chromium sources may be chromic acid, nitrates of chromium, hydroxides of chromium, ammonium chromate, ammonium dichromate, and chromium salts of organic acids such as oxalic acid and tartaric acid. Examples of the boron sources may be boric acid, ammonium borate, etc. The alkali metal may be Li, Na, K, Rb and Cs, and Na and K are preferable. Examples of the alkali metal sources may be alkali hydroxides, alkali carbonates, alkali nitrates and alkali salts of organic acids such as oxalic acid, tartaric acid and acetic acid. The sources for other metals may be metal salts of inorganic or organic acids, which are easily converted into metal oxides by heating in air.
The metal oxide catalysts are preferably supported on known carrier such as silica, alumina, etc., and preferably silica. Examples of silica used as the carrier include silica gel, colloidal silica, anhydrous silica, etc. as described, for example, in xe2x80x9cChemical Handbook, Applied Chemistry 1xe2x80x9d published by Maruzen (1986), pp. 256-258. The amount of alkali metal contained in the silica carrier should be considered in preparing a supported catalyst so that the alkali metal content falls within the range specified above. The amount of the carrier used is 20 to 80% by weight, preferably 40 to 70% by weight based on the weight of the supported catalyst.
The catalyst used in the present invention can be produced by known methods. For instance, the preparation of a supported catalyst comprising a silica carrier supporting Vxe2x80x94Crxe2x80x94Bxe2x80x94Moxe2x80x94Pxe2x80x94Na oxide catalyst is described below. An aqueous boric acid solution, sodium acetate and silica sol are successively added to an oxalic acid solution dissolving vanadium oxide and chromium oxide, thereby obtaining a slurry. A dissolving assistant such as polyhydric alcohols, xcex1-monocarboxylic acids and dioxycarboxylic acids may be added, if desired, to facilitate the dissolution of boric acid. The slurry is sprayed for drying and then further dried, if necessary, at 110 to 150xc2x0 C. The dried slurry is calcined at 400 to 700xc2x0 C., preferably 450 to 650xc2x0 C. for several hours or longer in a stream of air. Prior to the calcination, the dried slurry is preferably pre-calcined at 200 to 400xc2x0 C.
The catalyzed ammoxidation of the carbocyclic or heterocyclic compounds is carried out at 300 to 500xc2x0 C., preferably 330 to 470xc2x0 C. When the reaction temperature is lower than the above range, the conversion is low. When the reaction temperature is higher than the above range, the production of carbon dioxide, hydrogen cyanide, etc., is promoted, so that the yields of the aromatic or heterocyclic nitriles are reduced.
The reaction pressure is generally ordinary pressure. However, the reaction may be performed under increased or reduced pressure, if desired. The contact time between the reactant gas and the catalyst is usually in the range of 0.5 to 30 seconds, although varies depending upon kinds of raw materials, charged ratio between raw materials, air and ammonia, reaction temperature, etc.
In the present invention, the aromatic or heterocyclic nitriles may be collected by any known method, for example, by a method of cooling the reaction product gas to a temperature enough to precipitate the aromatic or heterocyclic nitriles, or a method of washing the reaction product gas with water or other suitable solvents.
Known catalysts do not undergo the deterioration with time in catalytic activity when water is not contained in the starting carbocyclic or heterocyclic compounds, oxygen-containing gas such as air and ammonia. However, when a non-negligible amount of water is contained, the sintering of the catalysts is promoted so that the catalyst activity is considerably deteriorated with time, thereby failing to stably produce the aromatic or heterocyclic nitriles.
Since the recovered ammonia contains a non-negligible amount of water, the catalyst activity is adversely affected by water. Although the water can be removed by distillation, adsorption, etc., these additional operations increase the production cost.
In the present invention, this problem in the prior art has been solved by the addition of alkali metal to the catalyst comprising oxides of V, Mo, Fe, etc. The addition of alkali metal maintains the catalyst strength such as wear resistance sufficiently high and prevents the deterioration of catalytic activity even when water enters into the reaction system accompanying the recycled ammonia, thereby stably producing the aromatic or heterocyclic nitriles at high yields over a long period of time.
The present invention will be described in more detail by reference to the following examples and comparative examples. However, it should be noted that the following examples are not intended to limit the invention thereto.